The invention relates to a luminaire comprising a panel of a light-transmitting material,
which panel includes a light emission window, a rear wall opposite said light emission window and edge surfaces which are situated between the light emission window and the rear wall,
at least one of the edge surfaces of the panel being light transmitting,
at least one light source being associated with the light-transmitting edge surface, and
in operation, light originating from the light source being incident on the light-transmitting edge surface and spreading in the panel.
The invention further relates to a light-emitting panel for use in the luminaire.
Such luminaires are known per se and are also referred to as edge lighting systems. They are applied, inter alia, in so-called luminous signs, among other things, for advertising purposes. They can also be used in guiding boards, such as xe2x80x9cexitxe2x80x9d-signs, in billboards, traffic lights, systems for guiding traffic flows and as (dashboard) lighting in vehicles. Said luminaires are further used as back lighting, for example, for display devices, such as LCD-devices. Said luminaires are used both as interior lighting and exterior lighting.
In such luminaires, a tubular low-pressure mercury-vapor discharge lamp, for example a (compact) fluorescent lamp (TL), is generally used as the light source, and the light emitted, in operation, by said light source is coupled into an optical waveguide which generally forms a relatively thin and flat panel, which panel is made, for example, of a synthetic resin or glass, and light being transported through the panel under the influence of total internal reflection. A text or a logo, for example a brand name, is engraved in the optical waveguide, the engraving lighting up, in operation, as a diffuse luminous area. The engraving is formed, for example, by etching or by suitably providing scratches. A text or a logo may alternatively be provided by applying a (light-scattering) layer on the panel. A text or a logo may alternatively be provided on a tape applied to the panel, which tape may exhibit differences in refractive index.
Such a luminaire may also be provided with an alternative light source in the form of a plurality of opto-electronic elements, also referred to as electro-optic elements, such as electroluminescent elements, for example light-emitting diodes (LEDs). These light sources are generally provided so as to be close to or abut against a light-transmitting edge surface of the panel, so that, in operation, light originating from the light source is incident on the light-transmitting edge surface and spreads into the panel.
From DE-A 38 33 315 an LED edge lighting system is known, which comprises one or more light-emitting diodes which are coupled via optical waveguides to a light-emitting panel to cause a light surface or light symbol provided in or on the light emission window to light up. This light surface or light symbol is provided as a light-scattering layer on the surface of the panel, or as a light-scattering recess in the surface of the panel.
A luminaire of the type mentioned above has various drawbacks. For example, only a part of the light in the panel contacting the light symbol is coupled out of the panel, and, in addition, a part of the light is emitted in the direction of the rear wall. Besides, the light symbol lights up like a diffusely luminescent area. As a result, the attractiveness of the luminaire is reduced.
It is an object of the invention to obviate the above drawbacks. The invention more particularly aims at providing a luminaire of the type mentioned in the opening paragraph, in which light is coupled out so as to obtain a specific light distribution.
To achieve this, the luminaire is characterized in accordance with the invention in that
in the panel a plurality of deformities is provided for coupling light out of the panel via the light emission window,
said deformities being clustered so as to form at least one light symbol, and
said cluster having a configuration which corresponds to the shape of the light symbol.
The measure in accordance with the invention causes the attractive effect, the appeal and the attention value of the luminaire in accordance with the invention to be increased. The term xe2x80x9cdeformitiesxe2x80x9d is to be taken to mean, in general, in the description and the claims of the current invention, means by means of which light can be coupled out of the panel. A deformity is an optical structure having a predetermined geometrical shape and dimensions. The use of deformities enables light to be coupled out of the panel in a well-defined manner. The light is coupled out in a predetermined direction, which direction may also depend upon the shape and the position of the deformity on the panel. This means, inter alia, that an observer who moves past the luminaire without specifically looking in the direction of the panel is struck at a certain moment xe2x80x9cfrom the corner of his eyexe2x80x9d by light emitted by the luminaire in accordance with the invention. This unexpected occurrence arouses the attention of the observer and xe2x80x9cforcesxe2x80x9d as it were the observer to look at the luminaire. This results in an increase of the attention value of the luminaire.
The deformities serve as a secondary light source.
An additional advantage of these deformities is that clusters of deformities can be selectively illuminated. By virtue thereof, it becomes possible to make different light symbols light up independently from each other and/or sequentially. By making light symbols light up alternately, using control electronics, by causing the clusters of deformities associated therewith to couple light out of the panel, light objects that move as it were can be obtained (for example a man who seems to be walking), or a text can be made visible by making the letters light up one after the other. Also various, colored light sources can be alternately switched on and off, so that a light symbol lights up in various colors. In this manner, the luminaire in accordance with the invention obtains dynamic lighting possibilities with a high attention value.
A further advantage of these deformities is that more light is coupled out of the panel, which leads to a directed reflection of these deformities and hence an improved brightness of the luminaire. To direct the light which is coupled out of the panel by these deformities, preferably, a boundary surface of the deformities is provided with a specularly reflecting surface, for example a reflecting layer of aluminium or silver, or a reflective multilayer coating. In an alternative, preferred embodiment, the deformities are shaped such that, in the deformities, total internal reflection causes the light to be coupled out of the panel. An important advantage of total internal reflection as a way of coupling light out of the panel is that it is not necessary to locally provide the deformities with a reflecting surface.
In the known luminaire, light incident on the diffusely reflecting light symbol when being reflected to and fro in the panel is emitted in all directions, for example also in the direction of the rear wall. As a result, the brightness of the luminaire in a direction transverse to the panel is lower than that of the light source, leading to a reduction of the attractiveness of the luminaire.
It is to be noted that the provision of a plurality of deformities to couple light out of a luminaire is known per se. In such edge lighting systems, a plurality of light-extracting so-called xe2x80x9cdeformitiesxe2x80x9d or xe2x80x9cdisruptionsxe2x80x9d are provided in the light-emitting panel. The shape and/or dimensions of these deformities may change gradually and/or the distance between the deformities in the panel may change gradually. However, the objective of such edge lighting systems is to obtain a light distribution which is as uniform as possible, said systems serving, in particular, as a lighting panel for, for example, (flat) display devices, such as, for example, liquid crystal display devices. The light distribution of the luminaire in accordance with the invention deliberately is not homogenous and not uniform. These (dynamic) deviations from a homogeneously and uniformly illuminated panel add to the attention value of the luminaire.
A preferred embodiment of the luminaire is characterized in accordance with the invention in that at least a first and a second edge surface are light-transmitting,
at least one first light source being associated with the first light-transmitting edge surface, and at least one second light source being associated with the second light-transmitting edge surface, and
in operation, a first cluster of deformities coupling out light originating from the first light source to form a first light symbol, and
in operation, a second cluster of deformities coupling out light originating from the second light source to form a second light symbol.
In the known luminaire, at a specific location on the panel only one specific light symbol (for example the letter xe2x80x9cPxe2x80x9d) can be made to light up or a collection of light symbols (for example the words xe2x80x9cACCESS DENIEDxe2x80x9d) can be made to light up simultaneously. In the above-mentioned embodiment of the luminaire in accordance with the invention, two light symbols (for example the letter xe2x80x9cExe2x80x9d and the letter xe2x80x9cAxe2x80x9d) or two collections of light symbols (for example the word xe2x80x9cEXITxe2x80x9d and the words xe2x80x9cNO ENTRYxe2x80x9d) can be made to light up on the panel independently of each other. In addition, these light symbols or collections of light symbols can locally overlap entirely or partly. Thus, in this embodiment it is possible to switch from one text to the other text. It is also possible to add text to an existing text (for example by replacing the term xe2x80x9cENTRYxe2x80x9d by xe2x80x9cNO ENTRYxe2x80x9d), or by providing a brand name or logo with a crown or with symbols in the form of, for example, stars, which additional light symbols can be switched on and switched off, depending on the requirements.
It is further possible in this embodiment of the luminaire in accordance with the invention that two light symbols or two collections of light symbols have different colors (for example a text or brand name which lights up in green and/or in blue, above which there is a star and/or a crown which lights up in red and/or yellow). By coupling out light by associating a first cluster of deformities with a first light source, and by coupling out light by associating a second or further cluster of deformities with a second or further light source, the number of lighting possibilities is increased substantially and the attractive value of the luminaire in accordance with the invention is substantially increased. In general, a plurality of panels whose light emission windows are arranged, for example, parallel to each other are necessary to make seemingly overlapping light symbols light up independently of each other. Such stacks of panels take up too much space, require much material, are relatively heavy and large and hence expensive.
To make sure that the light is coupled out of the panel so as to travel in (a) specific direction(s), the deformities are preferably arranged in the rear wall of the panel. If light, which is reflected to and fro by the panel, is incident on such a deformity or optical structure in the rear wall, reflection occurs, causing light to be sent towards the light emission window and leave the panel at the light emission window. In an alternative embodiment, the deformities are provided in or on the light emission window of the panel. These deformities may have, for example, a lens structure.
The shape, dimensions and location of the deformities influence the way in which light leaves the panel. For example, a preferred embodiment of the luminaire in accordance with the invention is characterized in that the shape of the deformity is selected from the group formed by a triangular prism, a tetrahedron, a quadrilateral pyramid and a cone. Such shapes are very suitable for coupling light out of the luminaire in various ways.
A deformity in the form of a triangular prism can very suitably be used to allow unobstructed passage of light in one direction and couple said light out of the panel in a direction transverse thereto. A favorable embodiment of the luminaire in accordance with the invention is characterized in that
the deformity is a triangular prism, a side face of the prism being provided transversely to the rear wall,
if the deformity forms part of the first cluster of deformities, ribs of the prism extend transversely to the direction wherein, in operation, the first light source emits light, and
if the deformity forms part of the second cluster of deformities, ribs of the prism extend transversely to the direction wherein, in operation, the second light source emits light.
In this embodiment, the triangular prisms are situated with a side face on or in the rear wall of the panel. In the embodiment described, the following effects occur. Light originating from the first light source is reflected at the side faces of the prisms of the first cluster of deformities, while light originating from the second light source is passed via the upper face and the lower face of the prisms of the first cluster. It is noted for clarity that side faces of a prism are situated between the ribs of the prism, while the upper face and the lower face are situated at the so-called end faces of the prism. Conversely, light originating from the second light source is reflected at the side faces of the prisms of the second cluster of deformities, while light originating from the first light source is passed via the side faces of the prisms of this second cluster. If only the first light source is switched on, then only the deformities forming part of the first cluster couple light out of the panel, which deformities thus form the first light symbol and cause it to light up. Correspondingly, only the deformities forming part of the second cluster couple light out of the panel, which deformities thus form the second light symbol and cause it to light up. If both light sources are switched on, then both clusters of deformities couple out light, thus forming both light symbols. If, in addition, the first and the second light sources couple light of different colors into the panel, then the light symbols having these different colors light up independently of each other. In this manner, a luminaire having a great attractive effect and a high attention value is obtained. By suitably switching on and off the light sources, a luminaire having dynamic lighting possibilities is obtained in this manner.
If, for example, the panel of a luminaire is triangular in shape, with light sources being associated with all three edge surfaces, and the ribs of the three types of triangular prisms extending transversely to the direction in which, in operation, the respective light sources emit light, then also the prisms of the other two clusters will reflect part of the light emitted by the first light source. In the case of a triangular panel, it is advantageous to employ deformities in the form of tetrahedrons. Each one of the side faces of a tetrahedron is then associated with one of the edge surfaces of the panel.
It is particularly favorable if the upper face and the lower face of the prisms are provided in a direction transverse to the rear wall. By virtue thereof, light which is reflected at the upper or the lower face of a prism as a result of the transition from or to such an upper or lower face, is emitted in the same, yet oppositely directed, direction. In this manner, such light cannot be coupled out of the panel. It is further very favorable if the side faces of the prisms exhibit total internal reflection.
The scope of protection of the invention also comprises a light-emitting panel provided with deformities for use in a luminaire as described in this description and the claims.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.